The Accreditation Council for Graduate Medical Education (ACGME) released rules effective July 1, 2003 that affected duty hours for all ACGME-accredited residency programs in all specialties. These rules represent the largest national effort to reduce medical errors since the publication of the Institute of Medicine's To Err is Human in 2000 and will directly impact the health care received by the 44% of patients cared for in teaching hospitals in the United States. By reducing sleep deprivation, the rules will likely have beneficial effects on patient safety and quality of care, but worsened continuity of care may counterbalance some of these benefits. This project will evaluate the effect of the duty hour rules on patient safety and quality of care, utilizing national data available though Medicare and pre-validated measures of quality including the AHRQ Quality Indicators. The primary aims of the project are to compare changes in the rate of mortality and failure-to-rescue (death after complications) in teaching hospitals and non-teaching hospitals before and after implementation of the ACGME work hour rules. Diagnoses studied will include all patients admitted for general, orthopedic, or vascular surgery and medical diagnoses of acute myocardial infarction, gastrointestinal bleeding, or stroke. The secondary aims are to examine differences in AHRQ Patient Safety Indicators (PSIs) before and after the rule change and to study how length of stay (LOS), the probability of a prolonged length of stay, and conditional length of stay (LOS once a stay is prolonged) changed in teaching vs. non-teaching hospitals. The study will be based on approximately 16 million surgical and medical admissions collected from the Medicare's MEDPAR data set spanning the years 1999-2003 (before the rule change) and 2003-2005 (after the rule change). We will use a multiple time series design with non-teaching hospitals as a control for teaching hospitals and will examine how effects differ in accordance with hospital dependence on residents (resident/bed ratio), program type and size, and hospitals' baseline financial status. The study will be powered to detect very small differences in these outcomes and will be able to test definitively whether the duty hour reform improved (or possibly worsened) patient safety and quality of care. Results from this study will be central to any future efforts to reduce errors in teaching hospitals through resident work hour reform.